Our long range goal is the complete elucidation of bioluminescence. This principally involves isolation, characterization, and structural determination of key components and understanding the mechanisms of light-emitting reactions. In this laboratory, a number of essential components have already been isolated, and, with some of them, the structures have been established. We have discovered a new type of system, termed "photoprotein," different from previously known "luciferin-luciferase" systems, first in the jellyfish Aequorea, then in the deep-sea shrimp Meganyctiphanes and a marine worm Chaetopterus followed by comparable discoveries by other investigators in various coelenterates and ctenophores. The photoprotein aequorin, which we discovered in Aequorea, emits light in aqueous solutions on addition of traces of Ca2 ions, and proved to be very useful in research on the role of Ca2 ions in biological systems. Our proposed research plan includes: (a) unequivocal elucidation of the pathway of luminescent reactions of the firefly, the ostracod Cypridina and the sea pansy Renilla, by carrying out the reactions with 18O2 gas and 13C-labelled luciferins (labelled at C equals O) followed by mass spectrometry of the product CO2; (b) structural study of a part of aequorin protein that surrounds the functional chromophore, by several techniques described in this proposal, to elucidate the mechanism in which the singlet excited state of the light-emitter is efficiently produced; (c) structural elucidations of the fluorescent compound "F" in Meganyctiphanes, the green fluorescent protein in Aequorea, the purple protein of the fresh water limpet Latia, and the luciferin of the Bermuda fireworm Odontosyllis; (d) elucidation of the luminescent reaction of the sea cactus Cavernularia; (e) study of the luminescent reaction of coelenterazine disulfate with singlet excited O2, in connection with the luminescence of the squid Watasenia.